Intro to Playbooks

About Playbooks

Playbooks are a completely different way to use ansible than in adhoc task execution mode, and are particularly powerful.

Simply put, playbooks are the basis for a really simple configuration management and multi-machine deployment system, unlike any that already exist, and one that is very well suited to deploying complex applications.

Playbooks can declare configurations, but they can also orchestrate steps of any manual ordered process, even as different steps must bounce back and forth between sets of machines in particular orders. They can launch tasks synchronously or asynchronously.

While you might run the main /usr/bin/ansible program for ad-hoc tasks, playbooks are more likely to be kept in source control and used to push out your configuration or assure the configurations of your remote systems are in spec.

There are also some full sets of playbooks illustrating a lot of these techniques in the ansible-examples repository. We’d recommend looking at these in another tab as you go along.

There are also many jumping off points after you learn playbooks, so hop back to the documentation index after you’re done with this section.

Playbook Language Example

Playbooks are expressed in YAML format (see YAML Syntax) and have a minimum of syntax, which intentionally tries to not be a programming language or script, but rather a model of a configuration or a process.

Each playbook is composed of one or more ‘plays’ in a list.

The goal of a play is to map a group of hosts to some well defined roles, represented by things ansible calls tasks. At a basic level, a task is nothing more than a call to an ansible module (see About Modules).

By composing a playbook of multiple ‘plays’, it is possible to orchestrate multi-machine deployments, running certain steps on all machines in the webservers group, then certain steps on the database server group, then more commands back on the webservers group, etc.

“plays” are more or less a sports analogy. You can have quite a lot of plays that affect your systems to do different things. It’s not as if you were just defining one particular state or model, and you can run different plays at different times.

For starters, here’s a playbook that contains just one play:

---
- hosts: webservers
  vars:
    http_port: 80
    max_clients: 200
  remote_user: root
  tasks:
  - name: ensure apache is at the latest version
    yum: name=httpd state=latest
  - name: write the apache config file
    template: src=/srv/httpd.j2 dest=/etc/httpd.conf
    notify:
    - restart apache
  - name: ensure apache is running (and enable it at boot)
    service: name=httpd state=started enabled=yes
  handlers:
    - name: restart apache
      service: name=httpd state=restarted

We can also break task items out over multiple lines using the YAML dictionary types to supply module arguments. This can be helpful when working with tasks that have really long parameters or modules that take many parameters to keep them well structured. Below is another version of the above example but using YAML dictionaries to supply the modules with their key=value arguments.:

---
- hosts: webservers
  vars:
    http_port: 80
    max_clients: 200
  remote_user: root
  tasks:
  - name: ensure apache is at the latest version
    yum:
      name: httpd
      state: latest
  - name: write the apache config file
    template:
      src: /srv/httpd.j2
      dest: /etc/httpd.conf
    notify:
    - restart apache
  - name: ensure apache is running
    service:
      name: httpd
      state: started
  handlers:
    - name: restart apache
      service:
        name: httpd
        state: restarted

Playbooks can contain multiple plays. You may have a playbook that targets first the web servers, and then the database servers. For example:

---
- hosts: webservers
  remote_user: root

  tasks:
  - name: ensure apache is at the latest version
    yum: name=httpd state=latest
  - name: write the apache config file
    template: src=/srv/httpd.j2 dest=/etc/httpd.conf

- hosts: databases
  remote_user: root

  tasks:
  - name: ensure postgresql is at the latest version
    yum: name=postgresql state=latest
  - name: ensure that postgresql is started
    service: name=postgresql state=running

You can use this method to switch between the host group you’re targeting, the username logging into the remote servers, whether to sudo or not, and so forth. Plays, like tasks, run in the order specified in the playbook: top to bottom.

Below, we’ll break down what the various features of the playbook language are.

Basics

---
- hosts: webservers
  remote_user: root

---
- hosts: webservers
  remote_user: root
  tasks:
    - name: test connection
      ping:
      remote_user: yourname

---
- hosts: webservers
  remote_user: yourname
  become: yes

---
- hosts: webservers
  remote_user: yourname
  tasks:
    - service: name=nginx state=started
      become: yes
      become_method: sudo

---
- hosts: webservers
  remote_user: yourname
  become: yes
  become_user: postgres

---
- hosts: webservers
  remote_user: yourname
  become: yes
  become_method: su

tasks:
  - name: make sure apache is running
    service: name=httpd state=running

tasks:
  - name: disable selinux
    command: /sbin/setenforce 0

tasks:
  - name: run this command and ignore the result
    shell: /usr/bin/somecommand || /bin/true

tasks:
  - name: run this command and ignore the result
    shell: /usr/bin/somecommand
    ignore_errors: True

tasks:
  - name: Copy ansible inventory file to client
    copy: src=/etc/ansible/hosts dest=/etc/ansible/hosts
            owner=root group=root mode=0644

tasks:
  - name: create a virtual host file for {{ vhost }}
    template: src=somefile.j2 dest=/etc/httpd/conf.d/{{ vhost }}

Action Shorthand

Ansible prefers listing modules like this in 0.8 and later:

template: src=templates/foo.j2 dest=/etc/foo.conf

You will notice in earlier versions, this was only available as:

action: template src=templates/foo.j2 dest=/etc/foo.conf

The old form continues to work in newer versions without any plan of deprecation.

Handlers: Running Operations On Change

As we’ve mentioned, modules are written to be ‘idempotent’ and can relay when they have made a change on the remote system. Playbooks recognize this and have a basic event system that can be used to respond to change.

These ‘notify’ actions are triggered at the end of each block of tasks in a playbook, and will only be triggered once even if notified by multiple different tasks.

For instance, multiple resources may indicate that apache needs to be restarted because they have changed a config file, but apache will only be bounced once to avoid unnecessary restarts.

Here’s an example of restarting two services when the contents of a file change, but only if the file changes:

- name: template configuration file
  template: src=template.j2 dest=/etc/foo.conf
  notify:
     - restart memcached
     - restart apache

The things listed in the notify section of a task are called handlers.

Handlers are lists of tasks, not really any different from regular tasks, that are referenced by a globally unique name. Handlers are what notifiers notify. If nothing notifies a handler, it will not run. Regardless of how many things notify a handler, it will run only once, after all of the tasks complete in a particular play.

Here’s an example handlers section:

handlers:
    - name: restart memcached
      service: name=memcached state=restarted
    - name: restart apache
      service: name=apache state=restarted

Handlers are best used to restart services and trigger reboots. You probably won’t need them for much else.

Roles are described later on, but it’s worthwhile to point out that:

• handlers notified within pre_tasks, tasks, and post_tasks sections are automatically flushed in the end of section where they were notified;
• handlers notified within roles section are automatically flushed in the end of tasks section, but before any tasks handlers.

If you ever want to flush all the handler commands immediately though, in 1.2 and later, you can:

tasks:
   - shell: some tasks go here
   - meta: flush_handlers
   - shell: some other tasks

In the above example any queued up handlers would be processed early when the meta statement was reached. This is a bit of a niche case but can come in handy from time to time.

Executing A Playbook

Now that you’ve learned playbook syntax, how do you run a playbook? It’s simple. Let’s run a playbook using a parallelism level of 10:

ansible-playbook playbook.yml -f 10

Ansible-Pull

Should you want to invert the architecture of Ansible, so that nodes check in to a central location, instead of pushing configuration out to them, you can.

The ansible-pull is a small script that will checkout a repo of configuration instructions from git, and then run ansible-playbook against that content.

Assuming you load balance your checkout location, ansible-pull scales essentially infinitely.

Run ansible-pull --help for details.

There’s also a clever playbook available to configure ansible-pull via a crontab from push mode.

Tips and Tricks

Look at the bottom of the playbook execution for a summary of the nodes that were targeted and how they performed. General failures and fatal “unreachable” communication attempts are kept separate in the counts.

If you ever want to see detailed output from successful modules as well as unsuccessful ones, use the --verbose flag. This is available in Ansible 0.5 and later.

Ansible playbook output is vastly upgraded if the cowsay package is installed. Try it!

To see what hosts would be affected by a playbook before you run it, you can do this:

ansible-playbook playbook.yml --list-hosts